Hi & welcome to KH. My best guess based on your attachment is that you want a cable cast on, does it somewhere tell you to use the provisional cast on? I think more info would be helpful. What are you making? Is it a sweater? Is it worked from the bottom? I think your garment is worked from the bottom but that is a guess. Maybe someone else will be able to tell more and help you better. I hope so. A link to the pattern, it's name and where you found it, even a picture of your project is generally helpful.
You can't knit the left sock first. Ever.